This invention relates to abrasive products with improved dimensional stability and particularly to fiber-backed abrasive discs.
In a conventional process for producing abrasive discs for general purpose abrading, a backing material that has been treated with a maker adhesive layer on a major surface is coated over the maker coat with abrasive grain and the coat is at least partially cured to adhere the grain to the coat. A size coat is then deposited over the grain to secure the grain in place and the size coat is cured. The backing material is usually in form of a large roll, called a "jumbo", such that the initial form of the abrasive material is a jumbo and this is given any necessary final cure while in the rolled position.
The maker and size coats are conventionally supplied by phenolic resins which require a protracted cure period, a portion of which is most frequently conducted while the material is in the jumbo form. When abrasive discs are the target product, the jumbo is unrolled and discs are cut from the roll. Not surprisingly the discs often have a slight curvature from the final cure that occurred in the jumbo. More importantly, when the backing is a fibrous material, such as a woven or stitch-bonded fabric or a cellulosic material, this is often sensitive to water content and changes in the moisture content of the surroundings, whether during manufacture of the discs or use of the finished item, can lead to the development of a distinct curl to the disc. Curling is usually caused by a mis-match of dimensional changes between the backing and the maker/grain layer when exposed to ambient moisture variations between the time the product was manufactured and when it is shipped to the final destination and unpacked for use by the customer. Usually the curling is more pronounced in the machine direction and this is attributed to anisotropic dimensional changes in the fiber backing. Attempts have been made to remedy this problem by controlling moisture content and degree of flexing. However curling will still occur as the discs are exposed to widely varying humidity conditions in different geographical locations.
There is therefore a need for a process that will produce dimensionally stable abrasive materials such as discs, wherein the stability is essentially independent of the relative humidity at the time of manufacture and use.